The main function of the human stereo system is to combine the monocular images, assigning a unique position in depth to each visible feature. In the last two decades, there have been two approaches to studying the binocular combination of signals from the two eyes: binocular contrast summation and stereo matching. Generally, research on stereo matching has ignored the contrast work, while studies of binocular contrast summation have failed to consider the role of stereo matching. Yet these two issues are intertwined. In dichoptic masking, a high contrast feature in one eye masks a weak contrast signal at retinal correspondence in the other eye. We have recently demonstrated that stereo matching operations can intervene to prevent dichoptic masking at, retinal correspondence. In the proposed research, we will use measurements of contrast thresholds to explore the operations underlying human stereo matching. We will test whether the constraints employed in computational stereo models are applicable to human vision. We will also re-examine dichoptic masking for local aperiodic targets, since much of the previous research has employed grating targets. Strabismic and anisometropic patients often suffer the loss of stereopsis due to the abnormal neural development associated with their condition. In amblyopia, the stronger normal eye of the amblyope suppresses signals from the weaker, abnormal eye; this suppression is sometimes modeled as a type of dichoptic masking. To understand the nature of the loss experienced by stereoanomalous observers, we will repeat many of our studies on stereo matching and dichoptic masking in mild anisometropic amblyopes.